Insight into gliding arc (GA) plasma reduction of CO₂ with H₂: GA characteristics and reaction mechanism

As an intermedia between cold and thermal plasmas, warm plasma generated by gliding arc (GA) discharge possesses high conversions and high energy efficiencies for CO₂ conversion. However, there is little understanding for the arc characteristics in CO₂-based atmosphere and reaction mechanism of CO₂ in GA plasma from experimental approach. For this purpose, a magnetically driven GA plasma with a constant length of arc is designed to study GA characteristics and reaction mechanism by changing H₂/CO₂ molar ratio (from pure CO₂ to pure H₂). In the entire range of H₂/CO₂ ratio, the arc channel shows a glow-like feature. The plasma parameters are arc temperature of 2200–3600 K, electron density of ∼1.6  ×  10¹⁴ cm⁻³ and electron temperature of ∼3 eV. From pure CO₂ to pure H₂, arc diameter decreases from 1.3 to 0.6 mm, whereas rotational frequency increases from 20 to 64 Hz. Based upon the optical emission spectra of CO, OH, H and O species, chemluminescence spectra of CO and O recombination and CO production rate detected online by gas chromatographs, the reaction mechanism at low and high H₂/CO₂ molar ratios is disclosed. (paper)